Updated Travis CI configuration and dependencies

[Pimm]

• Updated Travis CI configuration, including the removal of sudo: false.
• Updated dependencies (only dev dependencies were outdated).
• Fixed test.
• Removed stray publish logic from Travis CI configuration, as we aren't using that.
• Removed stray Husky dependency.

[Pimm]

Although I'm wondering why that test didn't fail before..

The expect is inside if (!orders.length). This test creates an order only if there are none (and only checks the ID if the order was created).

Tests previously ran with a different API key. An API key for an account which already had at least one order.

I do plan on reviewing all of these tests in the near future. They should behave consistent ‒ regardless of the payments/orders/customers which exist or do not exist on the test account.